Wavelength selection apparatus for use in various applications such as spectrometry, the demultiplexing/multiplexing of multiline laser beams, and so forth, includes an input prism and an output prism aligned along an optical axis, and at least one side mirror. A second side mirror spaced from the first side mirror on the opposite side of the optical axis may be provided, as well as end mirrors adjacent to the input and output prisms. An incoming beam incident upon the input prism is refracted so as to deflect and angularly disperse the various wavelengths present in the input beam, with the dispersing beam reflected from the first side mirror either directly to the output prism or with intermediate reflections from the second side mirror and the end mirrors before impinging upon the output prism. The output prism matches the input prism and deflects and recollimates the dispersed wavelengths to provide parallel output beams of different wavelengths spaced from one another. Selection of a desired wavelength in the output beam may be obtained by moving the input and output prisms with respect to each other axially until the desired output beam is moved to a position in which it passes through an aperture.